An optical network, such as a passive optical network (PON) as an example, often delivers voice, video and/or other data among multiple network nodes. In the case of a PON, the network nodes are often referred to as optical network terminals (ONTs). The PON can deliver data among multiple ONTs using a common optical fiber link. Passive optical splitters and combiners enable multiple ONTs to share the optical fiber link. An optical line terminal (OLT) transmits information downstream to the ONTs, and receives information transmitted upstream from the ONTs. Each ONT terminates the optical fiber link for a residential or business subscriber, and is sometimes referred to as a subscriber or customer premises node.
Each ONT is connected to one or more customer premises equipment (CPE) devices, which ultimately receive the voice, video and other data delivered via the PON. Examples of CPE devices include computers, telephones, television set-top boxes or the like. An ONT on a PON may receive traffic from several sources. Some sources may be commonly used among several ONTs on a PON. For example, several ONTs may access a common traffic flow associated with switched digital video (SDV) or other multicast streams. Other sources may produce traffic flows that are unique to an individual ONT. For example, an individual ONT may receive web content from an Internet service provider (ISP) or voice data from the public switched telephone network (PSTN).
To schedule delivery of data, such as requests for data stored on a server located in a public network, upstream from ONTs to OLTs over the shared or common optical fiber link, the OLT maintains a scheduler that grants each of the ONTs to which it connects (or, more specifically, so-called traffic containers or “T-conts” storing packets within each of the ONTs) a time slot during which each of the ONTs may transmit their respective upstream data to the OLT. In order to schedule these grants, the OLT may determine how much data each of the ONTs has to transmit upstream. In some instances, the OLT may issue a request to the ONTs for a report of how much data is stored to each of its one or more upstream queues. Those ONTs that support this form of status reporting may respond with an approximate amount of how much data is stored to these one or more upstream queues. For those ONTs that do not support status reporting, the OLT may grant each of these ONTs a set amount of time to transmit upstream and then monitor the amount of traffic sent upstream by these ONTs during their granted set amounts of time. However, in monitoring upstream traffic, the OLT may not proactively schedule time slots to accommodate the upstream data waiting at the monitored ONTs. Instead, the OLT may react to the data sent upstream by these ONTs that do not support status reporting. In this reactive mode, the OLT may fail to schedule an adequate number of time slots to accommodate the amount of data waiting to be sent upstream by the monitored ONTs, which may hamper network operation in certain instances.
In any event, based on the reported status and/or the monitored status, the OLT may determine an upstream grant map that grants each of these ONTs one or more time slots during which these ONTs may transmit upstream data to the OLT. The OLT may generate this upstream grant map in a manner that accommodates different levels of service and past delivery of service using, for example, a weighted round robin or weighted fair queuing algorithm. Typically, the OLT determines this upstream grant map after each scheduling round, which is typically a set period of time during which the OLT may receive status reports from or after determining a monitored amount of data to be transmitted by the ONTs. The OLT determines this grant map at the end of each scheduling round as the OLT may not otherwise have enough information to schedule time slots appropriately for each of the ONTs. The period of time during which the OLT has to determine this grant map after receiving the status reports during any given scheduling round and monitoring upstream data before the grant map has to be sent downstream to the ONTs is, for example, approximately 125 micro seconds (μs) in a gigabit PON (GPON). Considering that the OLT also takes into consideration different levels of service and past delivery of service, computing this grant map in this limited amount of time may require significant resources in terms of processing power and storage capacity.